New renderings reflect design changes at 1 World Trade Center as construction continues and the last steel beam is lifted into place.

This May, Skidmore, Owings & Merrill’s (SOM’s) 1 World Trade Center became the tallest building in New York, but as construction continues on the 1,776-foot-tall-tower, design changes are still taking place. A new set of renderings released this week shows a new façade design for the first 20 floors that form the podium of the building, and a new treatment of the spire.

Jordan Barowitz, director of external affairs for codeveloper The Durst Organization, says that the changes to the base—which were first announced last fall, and include replacing the planned-for prismatic glass with a façade made from glass fins—were necessary because “the prismatic glass couldn’t be manufactured.” A change in the geometry of the podium will eliminate the tapering at the corners of the structure; instead, the façade will be perpendicular to the ground plane. This “slightly different architecture at the corners” was chosen to accommodate the changes to the façade material, Barowitz says, but will not require any additional structure to be added.

The noticeable change to the spire, previewed in March, includes the elimination of the radome, the enclosure of interlocking triangular panels designed to cover the more-than-400-foot-tall structure. “The radome couldn’t be maintained,” Barowitz says. “It wasn’t possible to replace the panels if they became damaged.” Instead the structure of the spire will remain exposed. Another, less obvious, planned change to the spire is the lighting: there was discussion about illuminating the spire with incandescent fixtures, but the decision has made to proceed with LED lighting fixtures.

As to how the tweaks were determined, Barowitz notes that “we looked at a lot of different options, and this is what everyone liked. SOM came up with the redesign and it was something we thought was beautiful.”

Meanwhile, construction continues on the structure, with updates on the Port Authority of New York and New Jersey’s website saying that steel has risen to the 104th floor, the installation of the glass curtainwall has risen to the 79th floor, and concrete floors have been installed as high as the 92nd floor. Last Thursday, the final structural beam was lifted into place on the 104th floor—the highest level that will be occupied. That beam was signed by President Obama, First Lady Michelle Obama, Governors Andrew Cuomo of New York and Chris Christie of New Jersey, and Mayor Michael Bloomberg, among others, during a visit to the site earlier this summer.